A spread spectrum signal receiver comprises a radio signal processing unit, at least partly implemented in software running on a processor. The processing unit determines a candidate collection of subsets of signal sources from a group of potential sources, by the criterion that an anticipated processing intensity required to derive position/time related data from that subset is equal to or less than a maximum specified processing intensity. Each subset contains at least a minimum number of signal sources necessary to produce position/time related data. The processing unit also selects a set of preferred signal sources from a candidate subset, based on a highest estimated quality of the position/time related data attainable during a subsequent operating period for the receiver without exceeding the maximum specified processing intensity. During the subsequent operating period, the receiver receives spread spectrum signals from the selected set of signal sources and produces position/time related data therefrom.